This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This application is related to the continuation of our present NIH grant examining the nature of the movement signals in the cerebellum associated with visually-guided movements. These studies have shown how position, velocity and speed information are encoded in the discharge of cerebellar Purkinje cells and that manual tracking is composed of discrete subunits consisting of speed pulses highly correlated with the discharge of cerebellar Purkinje cells. We are investigating the processing of movement errors and how that error information is used to control movements both immediately and for long-term changes (i.e. motor learning). The first two Specific Aims of this study expand our testing of the hypothesis that the cerebellum is the site of an inverse dynamics model of the arm. Specific Aim 1 tests the hypothesis that the cerebellar nuclei are the output stage of an inverse dynamics model by examining the firing of interpositus and dentate neurons during a circular tracking task in which viscous and elastic force fields at varying magnitudes are applied to the hand. Specific Aim 2 examines whether Purkinje cell discharge is consistent with the output of an inverse dynamics model when force control or force feedback is used to perform the task. Specific Aims 3-5 test the hypothesis that Purkinje cell simple spike discharge is the output of a forward internal model of the arm that predicts the upcoming arm kinematics.